There hasn’t been a public poll released on Tuesday’s Arizona GOP Senate primary in more than a month, illustrating Sen. John McCain’s commanding position in the once white-hot race with former Rep. J.D. Hayworth.

Despite Hayworth’s dwindling poll numbers, the election is one of a few high-profile contests that voters will decide Tuesday, and it has been McCain’s most challenging re-election battle to date.

After spending less than $5 million on his previous two Senate campaigns combined, McCain has dropped a staggering $20 million so far this cycle, including $10 million from April through June and $3.5 million in July. Hayworth, with a much smaller network of donors, raised less overall than McCain spent last month.

McCain began airing radio ads in late 2009, as Hayworth was able to use his radio talk show as an outlet for criticism of McCain. By the time Hayworth resigned from his show in January, McCain had already aired three different ads.

Hayworth hammered McCain, a formerly self-described “maverick,” early and often on some of his more moderate stances that the conservative former Congressman hoped to capitalize on in the primary. The strategy had promise, as polling showed the two separated by 11 points just two months ago.

However, McCain recognized the threat early, defended and perhaps retooled his positions, and played some offense. By late July, McCain had led three straight polls by more than 20 points.

“Complete the danged fence,” McCain said as he walked along the Mexican border in one of the more-publicized political ads of the year. The ad caught notice because it appeared to be a change for the McCain who once headed up comprehensive immigration reform in the Senate.

McCain also took to the airwaves to slam Hayworth, who was campaigning against wasteful government spending, as a “huckster” for appearing in an infomercial offering ways to take advantage of federal grant money. Hayworth’s record in Congress was put on display as well, as the McCain campaign labeled him an “avid earmarker.”

Hayworth was unable to fully take the tea party mantle, as McCain touted the support of local tea party groups as well. Also backing McCain were a couple of conservative heavy hitters in former Alaska Gov. Sarah Palin, Rep. Jeff Flake (R-Ariz.) and Sen. Jon Kyl (R-Ariz.).

He also received considerable backing from state legislators, including those who differ with him on some of the issues.

“I endorsed Sen. McCain before J.D. even got in the race, and I would have done it anyway because the way it works back there is seniority,” said state Senate Majority Whip Steve Pierce (R). “I don’t agree with him 100 percent of the time, but I agree with him enough, and he’ll be able to go back and get things done for Arizona. That’s what we need right now.

“J.D. is fine,” Pierce added, “but he would’ve been a freshman in a broom closet down in the basement.”

Many conservatives, though, remain unconvinced that McCain has changed his moderate ways. Despite an endorsement from McCain in the 2006 gubernatorial race, Len Munsil, who founded a conservative think tank in the state, provided an early endorsement for Hayworth.

In a statement on his personal website Sunday, Munsil wrote that although he’s not a “McCain hater,” he endorsed Hayworth because McCain “has never been a consistent conservative” and “seemed at times to relish poking conservatives in the eye.”

“If Sen. McCain does prevail, here’s hoping we will see more opposition to Obamacare and illegal immigration,” Munsil wrote, “and no more votes for bailouts and other big government programs.”

There are other notable Congressional races in the state. The open 3rd district is up for grabs following the retirement of Rep. John Shadegg (R). The candidate with the most name recognition is Ben Quayle, son of former Vice President Dan Quayle.

Ben Quayle tripped in the last weeks of the campaign as revelations surfaced about his role as a contributing writer to a racy startup website that chronicled the Scottsdale, Ariz., nightlife. Quayle was an early frontrunner, but the stumble opened the door for the other top candidates in the race: businessman Steven Moak, former state Sen. Jim Waring and Paradise Valley Mayor Vernon Parker.

Running to take on Rep. Harry Mitchell (D) in the 5th district is 2008 nominee David Schweikert, whom Mitchell defeated by 9 points two years after knocking Hayworth out of Congress. Challenging Schweikert for the GOP nomination are physician Chris Salvino, businessman Jim Ward and former state Rep. Susan Bitter Smith, who also ran in 2008.

In the 8th district GOP primary, Iraq War veteran Jesse Kelly put up a stiffer fight than many expected against former state Sen. Jonathan Paton, whom Republicans in Washington see as a legitimate contender against Rep. Gabrielle Giffords (D).

Whoever wins the primary will enter the general election at a significant financial disadvantage, as Giffords has spent the primary season stocking her coffers.

In the 1st district, Rep. Ann Kirkpatrick (D) has less than $900,000 but remains well ahead of any of her potential Republican opponents. They include 2008 nominee Sydney Hay, whose personal wealth gave him a wide lead in the GOP primary money race. McCain won the 1st district in the 2008 presidential race with 54 percent, the same as George W. Bush four years earlier.